title: The osteogenic differentiation of PDLSCs is mediated through MEK/ERK and p38 MAPK signalling under hypoxia.
abstract: OBJECTIVE
  During orthodontic treatment and chronic periodontitis, the periodontal vasculature is severely impaired by overloaded mechanical force or chronic inflammation. This leads to the hypoxic milieu of the periodontal stem cell niche and ultimately affects periodontal tissue remodelling. However, the role of hypoxia in the regulation of periodontal ligament stem cell (PDLSC) behaviours still remains to be elucidated. The present study was aimed at investigating the effects of hypoxia on osteogenic differentiation, mineralisation and paracrine release of PDLSCs and further demonstrating the involvement of mitogen-activated protein kinase (MAPK) signalling in the process.
  
  
  METHODS
  First, PDLSCs were isolated and characterised. Second, the effects of different periods of hypoxia on PDLSC osteogenic potential, mineralisation and paracrine release were investigated. Third, extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 kinase activities under hypoxia were measured. Finally, specific MAPK inhibitors PD98059 and SB203580 were employed to investigate the involvement of two kinases in PDLSC osteogenesis under hypoxia.
  
  
  RESULTS
  Immunocytochemical staining and multilineage differentiation assays verified that the isolated cells were PDLSCs. Cell viability, alkaline phosphatase (ALP) activity, messenger RNA (mRNA) and protein levels of runt-related transcription factor 2 (Runx2) and Sp7, mineralisation and prostaglandin E2 (PGE2) and vascular endothelial growth factor (VEGF) release were significantly increased by hypoxia. ERK1/2 and p38 were activated in different ways under hypoxia. Furthermore, hypoxia-stimulated transcription and expression of the above-mentioned osteogenic regulators were also reversed by PD98059 and SB203580 to different degrees.
  
  
  CONCLUSIONS
  Exposure of PDLSCs to hypoxia affected their osteogenic potential, mineralisation and paracrine release, and the process involved mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) and p38 MAPK signalling.
authors.affiliation: State Key Laboratory of Oral Diseases, Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, No. 14, 3rd Section, Renmin South Road, Chengdu 610041, PR China.
authors.forename: Yeke
authors.initials: Y
authors.lastname: Wu
authors.forename: Yunqiang
authors.initials: Y
authors.lastname: Yang
authors.forename: Pu
authors.initials: P
authors.lastname: Yang
authors.forename: Yifei
authors.initials: Y
authors.lastname: Gu
authors.forename: Zhihe
authors.initials: Z
authors.lastname: Zhao
authors.forename: Lijun
authors.initials: L
authors.lastname: Tan
authors.forename: Lixing
authors.initials: L
authors.lastname: Zhao
authors.forename: Tian
authors.initials: T
authors.lastname: Tang
authors.forename: Yu
authors.initials: Y
authors.lastname: Li
mesh_terms: D000328:Adult; D000469:Alkaline Phosphatase / Q000378:metabolism; D015153:Blotting, Western; D002454:Cell Differentiation; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010012:Osteogenesis; D010513:Periodontal Ligament / Q000166:cytology* / Q000201:enzymology*; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D000076182:Sp7 Transcription Factor; D055153:Stem Cell Niche; D013234:Stem Cells / Q000201:enzymology*; D014157:Transcription Factors / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; C493709:RUNX2 protein, human; D000076182:Sp7 Transcription Factor; C478163:SP7 protein, human; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D000469:Alkaline Phosphatase; D015232:Dinoprostone
keywords: Hypoxia; MEK/ERK; Osteogenic differentiation; Periodontal ligament stem cells; p38 MAPK